Acoustic Characterization of Metal/Polymer Membrane Enclosures

摘要

Polyaniline, an inherently conducting polymer, was synthesized and fabricated as an acoustic membrane enclosure for the packaging of a MEMS-based acoustic microsensor. The packaging was designed to minimize environmental ambient impact, including dust and excess moisture, but maximize microphone performance. Free-standing films of emeraldine base polyaniline were doped with metal salts of aluminum acetoacetate, iron acetoacetate, copper acetoacetate, or titanium ethoxide. Polymer-metal hybrid compositions were analyzed by scanning electron microscopy (SEM) and deconvoluting X-ray photoelectron spectra (XPS) to discern interactions between metal atoms and polyaniline. Mechanical properties of the material, specifically the glass transition temperature and elastic and imaginary moduli, were measured by dynamic mechanical analysis (DMA) as a function of metal type, mechanical excitation frequency and temperature. The hybrid materials were then formed and shaped as flat membranes or as shaped domes of variable radii of curvature,, including hemispherical. Acoustic transmission properties of metal-doped planar and dome-shaped membranes were measured by insertion loss as a function of acoustic frequency between 100 to 2000 Hz in a plane wave tube. Results indicated an effect of metal type upon incorporation into polyaniline, which showed increases in mechanical stiffness and acoustic resonance frequency consistent with increased metal-polymer interaction. Acoustic performance was compared to a numerical model of sound transmission through hemispherical domes as a function of sound frequency, membrane structure, modulus of elasticity, thickness, and source angle of incidence.